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The pivotal role of AMP-activated protein kinase in the regulation of fatty acid metabolism in skeletal muscle

THE PIVOTAL ROLE OF AMP-ACTIVATED PROTEIN KINASE IN THE
REGULATION OF FATTY ACID METABOLISM IN SKELETAL MUSCLE
by
Marcia Jeanine Abbott
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(INTEGRATIVE AND EVOLUTIONARY BIOLOGY)
August 2010
Copyright 2010 Marcia Jeanine Abbott

The contents of this dissertation contain four experiments aimed at determining the role of AMP-activated protein kinase (AMPK) in the regulation of fatty acid (FA) metabolism in skeletal muscle.; The findings in the first study suggest a link between Ca2+ signaling, via CaMKK, and AMPKα2 activation in the regulation of glucose uptake and FA uptake and oxidation in perfused rat skeletal muscle contracting at moderate intensity. Additionally, the data obtained with the AICAR groups provide further evidence for the presence of a Ca2+-independent AMPK-dependent signaling cascade in the regulation of glucose uptake and FA uptake and oxidation. Furthermore, the GLUT4 and CD36 data indicate that the translocation of these transport proteins may be regulated via Ca2+-dependent and Ca2+-independent signaling. Together, these results suggest that during muscle contraction, AMP- and Ca2+-induced signaling cascades regulate muscle metabolism in part by converging at AMPK.; The data from the second study provide further evidence for the involvement of AMPKα2 in the regulation of substrate use during muscle contraction. Additionally, the results of this study suggest that while AMPKα2 is activated by caffeine-induced increases in intracellular [Ca2+], this activation is not essential to observe increases in substrate uptake and FA oxidation during caffeine treatment. These data also suggest a role for AMPK-independent Ca2+-dependent signaling in the regulation of substrate metabolism in skeletal muscle. However, physiologically active AMPKα2 appears to be necessary to record time-dependent changes in FA uptake and glucose uptake, that match levels of wild type mice, in contracting skeletal muscle. Indeed, one of the more interesting findings of this study is that AMPKα2 deficiency led to a reciprocal switch in FA and glucose uptake during the 20-min contraction protocol.; The data from the third study suggest an involvement of AMPKα2 in the regulation of insulin stimulated fatty acid metabolism both in control diet (CD) and high fat diet (HFD) mice. In contrast, it does not appear that AMPKα2 is necessary in the regulation of basal and/or insulin stimulated glucose uptake in CD and HFD mice. Additionally, these data suggest that AMPKα2 may be involved in the expression and activation of proteins shown to be associated with the regulation of substrate metabolism and insulin signaling, such as CPT1, Akt, SIRT1, and PTP1b. Finally, a role for AMPKα2, in skeletal muscle, in the regulation of IL6 and TNFα protein expression in adipose tissue was established, suggesting the existence of “cross-tissue talk.”; The data from the final study provide evidence for the involvement of AMPKα2 activity in the regulation of fatty acid metabolism following exercise training in control fed mice. In contrast, it does not appear that AMPKα2 activity is necessary for the alterations in fatty acid metabolism that occur with exercise training in high fat-fed mice. However, it does appear that AMPKα2 activity is necessary for the effects of training, while under high fat-fed conditions, on glucose uptake. Additionally, these data suggest that AMPKα2 may be involved in the activation of ERK1/2 but not JNK1/2 in high fat-fed mice under sedentary and endurance training conditions.; Taken together, the results from these four experiments solidify the role of AMPK signaling in the regulation of FA metabolism in skeletal muscle. Additionally, it was shown that AMPK may have alternative upstream activators, such as CaMKK during caffeine treatment. Further, AMPK signaling does appear to be involved in the development of insulin resistance under high fat feeding conditions in mice and AMPK appears to be essential in the exercise training effects that occur while on a high fat diet in mice.

THE PIVOTAL ROLE OF AMP-ACTIVATED PROTEIN KINASE IN THE
REGULATION OF FATTY ACID METABOLISM IN SKELETAL MUSCLE
by
Marcia Jeanine Abbott
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(INTEGRATIVE AND EVOLUTIONARY BIOLOGY)
August 2010
Copyright 2010 Marcia Jeanine Abbott